Formation Of Haloacetic Acids Represented As Disinfection By-products In Aquaculture Water

The aquaculture water usually contains endogenous organic matter represented by natural organic matter（NOM）and exogenous organic matter represented by fishery antibiotics.The results showed that the endogenous NOM and exogenous antibiotics in water could easily react with Chlorine disinfectants to form Halogenated Disinfection by-products（H-DBPs）with high carcinogenic haloacetic acids（HAAs）.In this paper,we discussed the kinetics of the transformation of endogenous NOM（humic acid,HA）and exogenous antibiotics（Sulfacetamide,SFA and sulfamethoxazole,SMX）during chlorination,and studied the potential of H-DBPs represented by HAAs.The research showed:（1）In the chlorination of freshwater,the concentration of available chlorine and water temperature can promote the removal of HA,but had a negative impact on the yield of HAAs.The degradation rate of HA was the highest under neutral p H condition,and the yields of HAAs were the lowest under alkaline condition.Because the Cl^-and Br^-provided halogen groups for the production of HAAs,a large number of Bromoacetic acids（Br-AAs）were produced in the chlorination of marine aquaculture water.In the process of freshwater disinfection,HA macromolecules were broken and oxidized into chlorophenols.Then chlorophenols were fully combined with Cl^-under the action of active chlorine to form toxic HAAs.（2）In the disinfection of aquaculture water,the reaction between SFA and available chlorine followed the quasi first order kinetic model.The results showed that the increase of chlorination dose and temperature could promote the degradation of SFA and the formation of chloroacetic acids（Cl-AAs）.Neutral p H was favorable for the degradation of SFA,while alkaline p H was more favorable for the formation of Cl-AAs.The common NH₄⁺ions inhibited the removal of SFA.In contrast,HCO₃^-ions and HA had little effect on the degradation of SFA.The presence of Br^-not only accelerated the degradation rate of SFA,but also led to the production of Br-AAs.In the Na Cl O disinfection of freshwater,the characteristic functional groups of SFA fell off and were further oxidized into intermediate products such as chloroanilines and chlorophenols.Then chlorophenols was further chlorinated to form toxic HAAs.（3）In the disinfection of aquaculture water,the reaction between SMX and available chlorine also followed the quasi first order kinetic model.The results showed that the increase of chlorination dose and temperature could promote the degradation of SMX and the formation of Cl-AAs.The degradation of SMX was most favorable when p H was about 6,and the formation of Cl-AAs also showed a trend of first increasing and then decreasing under the influence of p H.The common NH₄⁺ions inhibited the removal of SMX.In contrast,HCO₃^-ions and HA had little effect on the degradation of SMX.The presence of Br^-not only accelerated the degradation rate of SMX,but also led to the production of Br-AAs.In the Na Cl O disinfection system of freshwater,the characteristic functional groups of SMX breaked and and were further oxidized into intermediate products such as chloroanilines and chlorophenols.Then chlorophenols were fully combined with Cl^-under the action of active chlorine,and finally formed toxic HAAs.